powerpc/powernv: Reorder fields in struct pnv_phb

This moves those fields in struct pnv_phb that are related to PE
allocation around. No logical change.

Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>